Working on your clients' live stores
If you want to work on a live store without affecting it, then you have two options:
Option 1: Work with a development store
Download the theme from the Themes page in the live shop, and then upload it to your existing development store. Now you can work on a copy of the live shop’s theme in a dev environment.
When you're ready to launch the updated theme, download the theme from your development store and then upload it to the live shop as the primary theme.
Option 2: Use a Theme Editor
You can use Shopify Theme Kit to modify your theme with a local text editor of your choice. It then pushes your edits to your development store using our API.
Shopify supports multiple themes, so you can make a copy of your theme on the Themes page in your Shopify admin, and edit that unpublished theme.